If you’ve been scrutinizing the system for flaws, it probably didn’t take you long to find one. It’s the possibility of a dreaded “black swan event.”

Here's a plain english explanation of the Dai stablecoin: You give them your ether and they only pay out the dollar amount. They hold onto your ether until you pay them back the dollar amount. Meanwhile they arbitrage the difference.

It's literally this:

"Boy howdy - Joe says he'll take $15 but all I have is ether! By the time the money makes it to Joe it might be $15.50!"

"No problem, consumer! Give me your ether and I will give Joe $15, but only if he takes my shitcoin."

"...why don't I just go to a real exchange?"

"Because then I can't make money."

"...why can't I write my own smart contract that only dispenses what Joe is entitled to?"

Do you have examples of how this system can be used in day-to-day action. I kind of understand the blockchain and after reading this also how this "stablecoin" works but still have no clue how you can use this system and replace current things...